Heat treatment method of low alloy-stainless steel composite plate

Abstract

The invention discloses a heat treatment method of a low alloy-stainless steel composite plate. The heat treatment method comprises the steps of quenching, tempering and stress relief treatment. In the quenching step, the composite plate is placed in a roller hearth type heating furnace to be heated, an upper layer radiation heating pipe and a lower layer radiation heating pipe are distributed on the roller hearth type heating furnace, a stainless steel coating of the composite plate is placed upwards, and a low-alloy base layer is placed downwards to be in contact with a heating furnace roller way; the initial temperature of the upper-layer radiation heating pipe and the lower-layer radiation heating pipe is set to be 880-890 DEG C, after heat preservation is carried out for 1.2-1.5 min / mm according to the total thickness, the temperature of the upper-layer radiation heating pipe is rapidly increased to 1000-1050 DEG C, the temperature of the lower-layer radiation heating pipe is kept unchanged, heat preservation is carried out for 1.0-2.0 min / mm according to the thickness of a stainless steel coating, and then the steel plate is discharged out of the furnace and enters a roller hearth type quenching machine to be cooled. The stainless steel layer obtained through the method is good in corrosion resistance and free of cracks after being bent through intergranular corrosion, the tensile strength of the steel plate is larger than or equal to 630 MPa, and the impact energy at the temperature of-40 DEG C is 200 J or above.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment, and in particular relates to a heat treatment method for a low alloy-stainless steel composite plate. Background Art

[0002] Low alloy-stainless steel composite plate has both the excellent mechanical properties of the base low alloy steel and the excellent corrosion resistance of the cladding stainless steel. It can also save precious alloy elements and reduce costs. It is widely used in the fields of petroleum, chemical industry, nuclear power, etc., with great economic and social benefits. Stainless steel composite plate not only realizes the complementary performance advantages of stainless steel and carbon steel, but also reduces costs and saves precious metal elements in stainless steel. Replacing pure stainless steel with stainless steel composite plate can save 1 / 3 of the raw material cost in related processing and manufacturing.

[0003] However, due to the different materials of the stainless steel composite plate coating and the base layer, the thermal conductivity, thermal expansion coefficient, and organizational transformation during heat treatment are different, which can easily lead to deformation during quenching heat treatment, increasing the difficulty of production. In addition, the heating process temperature of the low-alloy base layer and the coating stainless steel is different. In order to avoid heating the coating stainless steel in the sensitized zone, the temperature is often higher; the sensitized zone will cause chromium carbides to precipitate along the grain boundary of the coating stainless steel side, resulting in chromium-poor coating grain boundaries, which will cause intergranular corrosion of the stainless steel composite plate, thereby weakening the corrosion resistance of the coating.

[0004] In order to obtain a stainless steel composite plate with good base toughness and excellent coating corrosion resistance, an appropriate heat treatment process system is required to optimize the comprehensive performance of the composite plate. Summary of the invention

[0005] The present invention aims to provide a heat treatment method for a low alloy-stainless steel composite plate, which can solve the problems of easy deformation of the composite plate during quenching, difficulty in matching the strength and toughness of the base layer, and poor corrosion resistance of the coating.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A heat treatment method for a low alloy-stainless steel composite plate includes quenching, tempering and stress relief treatment.

[0007] Furthermore, in the quenching described in the present invention, the composite plate is placed in a roller bottom heating furnace for heating. The roller bottom heating furnace is provided with upper and lower layers of radiation heating tubes. The stainless steel coating of the composite plate is placed upward, and the low alloy base layer is placed downward to contact the heating furnace roller. The initial temperatures of the upper and lower layers of radiation heating tubes are both set to 880°C to 890°C. After being kept warm for 1.2 to 1.5 min / mm according to the total thickness, the temperature of the upper radiation heating tube is rapidly increased to 1000 to 1050°C, and the temperature of the lower radiation heating tube remains unchanged. It is kept warm for 1.0 to 2.0 min / mm according to the thickness of the stainless steel coating, so that the stainless steel layer is fully dissolved, chromium carbides are reduced, and corrosion resistance is improved. Because the base temperature is not high, the grains will not grow excessively, laying a structural foundation for the strength and toughness of the base layer.

[0008] Furthermore, in the quenching of the present invention, the composite plate after insulation is taken out of the furnace and cooled in a roller bottom quenching machine. The water pressure of the high-pressure section of the roller bottom quenching machine is 0.8-1MPa, the upper and lower water ratio is (1.2-1.5): 1, and the roller speed of the high-pressure section is controlled at 3-5m / min. In this step, the low alloy base layer obtains a martensite or bainite structure, and the cladding stainless steel is cooled quickly, which can reduce the time of passing through the sensitization zone during the cooling process, reduce the precipitation of chromium carbides, and improve the corrosion resistance of the coating. In addition, by setting a reasonable upper and lower water ratio, the stress deformation caused by the different organizational transformations of the low alloy base layer and the cladding stainless steel during the cooling process is reduced.

[0009] Furthermore, in the quenching of the present invention, the composite plate is cooled in the low-pressure section for 10 to 15 minutes after passing through the high-pressure section of the quenching machine, so as to further remove the heat of the composite plate and ensure that the composite plate is cooled thoroughly.

[0010] Furthermore, the tempering of the present invention is carried out in a car bottom furnace, the charging temperature is less than 300°C, and after heating to 400°C, it is kept warm for 1.5-2min / mm according to the total thickness, the purpose of which is to ensure that the composite plate is heated through before entering the stainless steel sensitization temperature, and then quickly heated to 660-680°C, kept warm for 3.5-4.0min / mm according to the thickness of the base layer, and then water-cooled after leaving the furnace. The purpose of water cooling is to reduce the residence time of stainless steel in the sensitization temperature zone as much as possible and improve corrosion resistance.

[0011] Furthermore, before tempering the composite plate of the present invention, a cover plate is added above the cladding stainless steel, the thickness and size of the cover plate are consistent with the low alloy base layer, the cover plate is sealed around the composite plate, and the stainless steel layer is sandwiched in the middle, mainly to minimize the effect of tempering on the precipitation of carbides of chromium in the stainless steel cladding layer and improve corrosion resistance.

[0012] Furthermore, in the stress relief treatment of the present invention, residual stress exists in the composite plate after tempering and water cooling, and the composite plate is heated to 400±10°C for a holding time of not less than 4 min / mm, and then air-cooled.

[0013] Furthermore, the method of the present invention is applicable to low alloy-stainless steel composite plates formed by explosive composite or rolling composite.

[0014] The composite board obtained by the method of the present invention has a tensile strength of ≥630MPa on the surface of the base layer and at 1 / 2 of the plate thickness, an average impact energy of >200J at -40°C at 1 / 4 of the plate thickness, a non-plastic transition temperature of ≤-30°C, and a shear strength of 380-430MPa; there is no crack after bending by intergranular corrosion, and the plate straightness satisfies ≤6mm / m.

[0015] The inventive principle and beneficial technical effects of the technical solution of the present invention are: During quenching, different temperatures are set for the stainless steel layer and the low alloy base of the composite steel plate, which can ensure that the stainless steel layer is fully dissolved and prevent the low alloy matrix from growing grains. By setting a suitable upper and lower water ratio and roller speed, the quenching deformation of the composite plate can be reduced. Water cooling can enable the base layer to obtain martensite or bainite structure, laying the organizational foundation for obtaining a good strength and toughness match. At the same time, water cooling of the stainless steel layer shortens the residence time in the sensitization zone, which can reduce the precipitation of chromium carbides and improve corrosion resistance. During tempering, the stainless steel layer is reduced by adding a cover plate and water cooling to increase corrosion resistance. The base layer obtains a good strength and toughness match through tempering, and finally the deformation of the composite plate is reduced through stress relief treatment. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0017] The low alloy-stainless steel composite plate of this embodiment is obtained by explosive composite method, the base material is SA533GrBCL1, the thickness is 58mm, the cladding stainless steel is 304, the thickness is 6mm; the heat treatment method of the composite plate is as follows: (1) Quenching The SA533GrBCL1-304 composite plate is placed in a roller bottom heating furnace for heating, with the 304 stainless steel layer facing upward and the SA533GrBCL1 base layer facing downward and contacting the roller; the roller bottom heating furnace is provided with upper and lower layers of radiation heating tubes, and the temperatures of the upper and lower layers of radiation heating tubes are both set to 880°C at the initial stage. After the total thickness is 64mm and the temperature is kept for 1.5min / mm, the temperature of the upper radiation heating tube is quickly increased to 1000°C, and the stainless steel 304 thickness is kept for 1min / mm according to the thickness of 6mm, and the stainless steel composite layer is further dissolved; after the insulation, the composite plate is taken out of the heating furnace and quenched in a roller bottom quenching machine. The water pressure in the high-pressure section of the quenching machine is 1MPa, the upper and lower water ratio is 1.5:1, and the roller speed in the high-pressure section is controlled at 3m / min. After passing through the high-pressure section, the composite plate is further cooled in the low-pressure section, and the water pressure in the low-pressure section is 0.5MPa. It is cooled for 15 minutes to further take away the heat of the composite plate and ensure that the composite plate is cooled thoroughly.

[0018] (2) Tempering After quenching, a 58mm thick cover plate is added on top of the cladding stainless steel of the composite plate. The length and width of the cover plate are consistent with the low-alloy substrate. The cover plate and the composite plate are sealed on all sides, sandwiching the 304 stainless steel layer in the middle.

[0019] Tempering is carried out in the car bottom furnace with a loading temperature of 200℃. After heating to 400℃, it is kept warm for 1.5min / mm according to a thickness of 64mm. Then it is quickly heated to 680℃. The holding time is calculated according to the base thickness of 58mm, the insulation coefficient is 3.5min / mm, and then it is taken out of the furnace and water-cooled.

[0020] (3) Stress relief treatment The cover plate was removed, the composite plate was subjected to stress relief treatment, the composite plate was heated to 410°C, kept warm for 4.5 min / mm, and then air-cooled.

[0021] The composite plate of this embodiment was subjected to shear, tensile, impact, and drop hammer tests, and the corrosion resistance of the coated stainless steel was subjected to an intergranular corrosion test according to GB / T4334. After bending, no cracks were observed under a 10x magnifying glass, and the corrosion resistance was good; the tensile strength of the base SA533GrBCL1 surface and 1 / 2 of the plate thickness was 630 to 680 MPa, the average impact energy at -40°C at 1 / 4 of the plate thickness was 280 J, the no-plastic transition temperature was -55°C, the shear strength was 430 MPa, and the performance was good; the straightness of the composite plate was 4 mm / m. Example 2

[0022] The low alloy-stainless steel composite plate of this embodiment is obtained by rolling composite method, the base material is SA738GrB, the thickness is 23mm, the cladding stainless steel is 316L, the thickness is 3mm; the heat treatment method of the composite plate is as follows: (1) Quenching The SA738GrB-316L composite plate is placed in a roller bottom heating furnace for heating, with the 316L stainless steel layer facing upward and the SA738GrB base layer facing downward and contacting the roller; the roller bottom heating furnace is provided with upper and lower layers of radiation heating tubes, and the initial upper and lower radiation heating tube temperatures are both set to 890°C. After insulation for 1.2 min / mm according to the total thickness of 26 mm, the temperature of the upper radiation tube is quickly increased to 1050°C, and insulation for 2 min / mm according to the thickness of 316L stainless steel of 3 mm is performed, and the stainless steel composite layer is further dissolved; after insulation, the composite plate is taken out of the heating furnace and cooled in a roller bottom quenching machine. The water pressure in the high-pressure section of the quenching machine is 0.8 MPa, the upper and lower water ratio is 1.2:1, and the roller speed in the high-pressure section is controlled at 5 m / min. After passing through the high-pressure section, the composite plate is further cooled in the low-pressure section, and the water pressure in the low-pressure section is 0.5 MPa. It is cooled for 10 minutes to further remove the heat of the composite plate and ensure that the composite plate is cooled thoroughly.

[0023] (2) Tempering After quenching, a 23mm thick cover plate is added on top of the cladding stainless steel. The length and width of the cover plate are consistent with the low-alloy substrate. The cover plate and the composite plate are sealed on all sides, sandwiching the 316L stainless steel layer in the middle.

[0024] Tempering is carried out in the car bottom furnace with the loading temperature of 280℃. After heating to 400℃, it is kept warm for 2min / mm according to the thickness of 26mm. Then it is quickly heated to 660℃. The holding time is calculated according to the base thickness of 23mm. The insulation coefficient is 4.0min / mm. Then it is taken out of the furnace and water-cooled.

[0025] (3) Stress relief treatment The cover plate was removed, the composite plate was subjected to stress relief treatment, the composite plate was heated to 390°C, kept warm for 4.5 min / mm, and then air-cooled.

[0026] The composite plate of this embodiment was subjected to shear, tensile, impact, and drop hammer tests, and the corrosion resistance of the coated stainless steel was subjected to an intergranular corrosion test according to GB / T4334. After bending, no cracks were observed under a 10x magnifying glass, and the corrosion resistance was good; the tensile strength of the base SA738GrB surface and 1 / 2 of the plate thickness was 720-780 MPa, the average impact energy at -40°C was 220 J, the no-plastic transition temperature was -35°C, the shear strength was 380 MPa, and the performance was good; the straightness of the composite plate was 6 mm / m. Example 3

[0027] The low alloy-stainless steel composite plate of this embodiment is obtained by rolling composite method, the base material is 18MND5, the thickness is 48mm, the cladding stainless steel is 316L, the thickness is 5mm; the heat treatment method of the composite plate is as follows: (1) Quenching The 18MND5-316L composite plate is placed in a roller bottom heating furnace for heating, with the 316L stainless steel layer facing upward and the 18MND5 base layer facing downward and contacting the roller; the roller bottom heating furnace is provided with upper and lower layers of radiation heating tubes, and the initial upper and lower radiation heating tube temperatures are both set to 885°C. After insulation for 1.4 min / mm according to the total thickness of 53 mm, the temperature of the upper radiation tube is quickly increased to 1030°C, and insulation for 1.5 min / mm according to the thickness of 5 mm of stainless steel 316L is performed, and the stainless steel composite layer is further dissolved; after insulation, the composite plate is taken out of the heating furnace and cooled in a roller bottom quenching machine. The water pressure in the high-pressure section of the quenching machine is 0.9 MPa, the upper and lower water ratio is 1.3:1, and the roller speed in the high-pressure section is controlled at 4 m / min. After passing through the high-pressure section, the composite plate is further cooled in the low-pressure section, and the water pressure in the low-pressure section is 0.5 MPa. The cooling takes 12 minutes to further remove the heat of the composite plate and ensure that the composite plate is cooled thoroughly.

[0028] (2) Tempering After quenching, a 48mm thick cover plate is added on top of the cladding stainless steel. The length and width of the cover plate are consistent with the low-alloy substrate. The cover plate and the composite plate are sealed on all sides, sandwiching the 316L stainless steel layer in the middle.

[0029] Tempering is carried out in the car bottom furnace with the loading temperature of 220℃. After heating to 400℃, it is kept warm for 1.8min / mm according to the thickness of 53mm. Then it is quickly heated to 670℃. The holding time is calculated according to the base thickness of 48mm. The insulation coefficient is 3.8min / mm. Then it is taken out of the furnace and water-cooled.

[0030] (3) Stress relief treatment The cover plate was removed, the composite plate was subjected to stress relief treatment, and the composite plate was heated to 400°C, kept warm for 4.6 min / mm, and then air-cooled.

[0031] The composite plate of this embodiment was subjected to shear, tensile, impact, and drop hammer tests, and the corrosion resistance of the coated stainless steel was subjected to an intergranular corrosion test according to GB / T4334. After bending, no cracks were observed under a 10x magnifying glass, and the corrosion resistance was good; the tensile strength of the base layer 18MND5 surface and 1 / 2 of the plate thickness was 650-690 MPa, the average impact energy at -40°C was 230 J, the no-plastic transition temperature was -50°C, the shear strength was 410 MPa, and the performance was good; the straightness of the composite plate was 5 mm / m.

Claims

1. A heat treatment method for a low alloy-stainless steel composite plate, characterized in that: It includes quenching, tempering and stress relief treatment; for the quenching, the composite plate is placed in a roller bottom heating furnace for heating, the roller bottom heating furnace is provided with an upper and lower layer of radiation heating tubes, the stainless steel coating of the composite plate is placed upward, and the low alloy base layer is placed downward to contact the heating furnace roller; the initial temperatures of the upper and lower layers of radiation heating tubes are both set to 880°C to 890°C, and after being kept warm for 1.2 to 1.5 min / mm according to the total thickness, the temperature of the upper radiation heating tube is rapidly increased to 1000 to 1050°C, and the temperature of the lower radiation heating tube remains unchanged, and is kept warm for 1.0 to 2.0 min / mm according to the thickness of the stainless steel coating, and then taken out of the furnace and enters the roller bottom quenching machine for cooling.

2. A heat treatment method for a low alloy-stainless steel composite plate according to claim 1, characterized in that: The water pressure in the high-pressure section of the roller bottom quenching machine is 0.8-1 MPa, the upper and lower water ratio is (1.2-1.5):1, and the roller speed in the high-pressure section is controlled at 3-5 m / min; after the composite plate passes through the high-pressure section of the quenching machine, it is cooled in the low-pressure section for 10-15 minutes.

3. The heat treatment method of a low alloy-stainless steel composite plate according to claim 1, characterized in that: The tempering is carried out in a car bottom furnace with a charging temperature of less than 300°C. After heating to 400°C, it is kept warm for 1.5-2min / mm according to the total thickness, then quickly heated to 660-680°C, kept warm for 3.5-4.0min / mm according to the thickness of the base layer, and then cooled with water after being taken out of the furnace.

4. The heat treatment method of a low alloy-stainless steel composite plate according to claim 1, characterized in that: Before tempering the composite plate, a cover plate is added above the cladding stainless steel. The thickness and size of the cover plate are consistent with the low alloy base layer. The cover plate is sealed around the composite plate to sandwich the stainless steel layer in the middle.

5. The heat treatment method of a low alloy-stainless steel composite plate according to claim 1, characterized in that: The stress relief treatment is to heat the composite plate to 400±10° C. for a holding time of not less than 4 min / mm, and then air cool it.

6. The heat treatment method of a low alloy-stainless steel composite plate according to claim 1, characterized in that: The method is applicable to a low alloy-stainless steel composite plate formed by explosive cladding or rolling cladding.

7. The heat treatment method of a low alloy-stainless steel composite plate according to claim 1, characterized in that: The composite board obtained by the method has a tensile strength of ≥630MPa on the surface of the base layer and at 1 / 2 of the board thickness, an average impact energy of >200J at -40°C at 1 / 4 of the board thickness, a non-plastic transition temperature of ≤-30°C, and a shear strength of 380-430MPa; no cracks after bending by intergranular corrosion, and the board shape straightness satisfies ≤6mm / m.